(1) Field of the invention
This invention relates to plain bearings and process for manufacturing same, in which a resinous cylinder as a sliding member is integrally combined with a metal cylinder.
(2) Description of the prior art
Conventionally, the plain bearings employing a resinous member include, e.g., a purely resin-made bearing, a winding bushing type bearing, a metal bearing having jointed a resinous member into the interior of a metal bush, etc.
Referring first to the purely resin-made bearing, a thinly formed resinous cylinder is inferior in strength, so that a thickly formed resinuous cylinder is used at present. However, the disadvantage of the latter is that after it has been fixed in a housing, the shrinkage of the internal diameter thereof becomes large due to the temperature variation, thereby it is impossible to set a clearance in a radial direction relative to a shaft to no more than 50 .mu.m. Accordingly, the rotation accuracy of the thickly formed cylinder is inferior and its initial abrasion is enlarged.
Referring to the winding bushing type bearing, it is, e.g., a cylindrical metal plate of which inner surface is coated with a preferred resin. The inaccuracy of right circularity of this bearing is within more or less 50 .mu.m and it requires a clearance gap of more than 50 .mu.m. Accordingly, the accuracy of this type of bearing is not so high.
Referring to the metal bearing having jointed a resinous cylinder, its manufacturing process has several defects and needs a time-consuming work. For example, when the resinous member is made of polytetrafluoroethylene, it is impossible to use any adhesive, so that the portion of bonding the resinous cylinder with the metal bush must be treated chemically. The task of this invention is to remove the aforesaid disadvantages of the conventional art.